How to make 3 quadrant sphere?
Rounded color values
When you need exact colors, you wouldn't want to use rounded values. To be exact, open your reference in the Image Editor and use the Eyedropper in your RGB node to pick the color.
Make sure, your scene doesn't use Filmic log encoding or any viewer LUTs, stay in sRGB the whole time, to maintain color fidelity.

Emission and diffuse combination
As @lucas-leme suggested, the emission shader gives you the exact values from your reference. But your image will look very flat. Create a second renderlayer, don't change any settings, just add a diffuse white material to the material override slot of the second render layer. In the compositor, set up the nodes as shown below, and clamp the diffuse pass down, so it is almost completely white and only contains the core shadows. Multiply this layer over the Emission pass.

please let me know if this helped, or if something is unclear. Here is my blend:

you need to render first, to see the compositing nodes at work.